The invention relates to a particle detection system in particular such a system comprising an impedance particle detector and fluorescence detector.
It is known to detect particles such as blood cells or yeast cells for example within a sample by passing the particles through a narrow orifice and detecting variations in the impedance across the orifice. Additionally, it is known to dye or stain samples with a suitable fluorescent dye and then illuminate the particles with a suitable source of light such as laser light of a fundamental frequency and thereafter determine the nature of the particles by the fluorescence signal emitted from the particles.
However, such known systems are very complex, costly, require continuous adjustment and are limited in terms of the minimum size of particles that can be detected. Accordingly, the invention seeks to improve impedance and fluorescent particle detection systems preferably making them more economical to manufacture and/or more efficient to operate. An object is to simplify the optical system and integrate the optics with the impedance system, especially by using an orifice plate as part of the fluorescence and impedance systems.
According to one aspect of the invention there is provided a combined impedance and fluorescence particle detection system comprising an optically transmissive plate having an orifice for the flow of particles therethrough, a light source which operably directs light on a particle at the orifice, and a light detector positioned so as to detect light which is emitted by the particle, and wherein the plate acts as a waveguide to direct light along part of its path between the light source and light detector. Beneficially therefore the plate comprises an orifice to effect the impedance measurement which plate also acts as a waveguide for part of the optical system. For example light can be transmitted from the orifice to a detector via the plate and/or to the orifice via the plate from a light source.
The direction of flow of particles passes through the plate, however, at least part of the light path between the source and detector can be in different direction with respect to the particle flow direction. In one particular form, light is projected from the light source substantially in line with the particle flow direction and the light detector is substantially at right angles thereto. In another form, the source and detector are substantially in line, therefore on opposite sides of the orifice plate.
Preferably the system is operable at two or more fundamental light frequencies to observe fluorescence. The light source can comprise at least one individual unit which emits light at different frequencies. Also or alternatively, more than one light source is provided enabling use of two different wavelengths of light. Beneficially this enables different properties of the particles to be measured. Preferably a detector is provided for each light source in order to determine the fluorescence at a given wavelength.
In a preferred form, a light source and/or a light detector is optically coupled to the orifice plate. The light source and/or detector can be directly optically coupled to the orifice plate. However, preferably the light detector can be directly optically coupled to a filter which is directly optically coupled to the orifice plate. Preferably the plate comprises a substantially straight edge for attachment of or coupling of the light sources and/or light detectors. In preferred forms, the orifice plate is polygonal especially of quadrilateral, hexagonal or octagonal shape. None, one or more, indeed all, edges of the orifice plate can carry a light source or detector. The plate can also be disc shaped.
To optimise efficiency of light transfer to the detector the waveguide properties of the plate are preferably optimised. The plate surfaces such as faces and/or edges can be treated so as to increase internal reflections within the plate. For example, the faces and/or edges can be coated such as with silver or aluminium.
In a preferred form, at least part of the plate edge is so treated so as to increase reflections towards the detector. In a preferred form both faces of the plate are partially treated so as increase internal reflections.
Accordingly, fluorescent light initially scattered away from the detector can be reflected by the silvered edge back towards the detector.
Preferably, the orifice is located in a region of relatively high concentration of internally reflected light, possibly a focal point of the plate. For example, for a disc-shaped plate this can be a central position or where coated surfaces are used, an off-centre position. Combinations of the following three features are possible (to provide six possibilities): the orifice is positioned at a point of increased concentration of internal reflections within the plate, one or more edges of the plate are treated especially by coating to increase internal reflection, one or more faces of the plate are treated such as by metallic coating to increase internal reflection.
The plate for example can be a ruby, quartz or sapphire crystal, or other optically transparent medium. Preferably the refractive index of the plate is higher than saline or other media such as diluent used to carry or dilute the sample particles. Preferably, the surface finish on the plate is smooth to a quarter wavelength.
Preferably a filter is positioned between the plate and the detector in order to attenuate frequencies other than the fluorescence emission frequency from the particles. Accordingly, the filter is preferably a band pass filter wherein the optimum transmission is based on the emission frequency from the particles which is of course shifted away from the fundamental frequency of the light source and or the characteristics are chosen to maximise the difference in attenuation between the emissive frequency from the particles and the fundamental frequency of the light source.
Preferably, the optically transmissive orifice plate is made of one piece but can be made of components or parts such as a first orifice carrying part mounted in a larger mount or slide part to improve handling and positioning of the plate within the particle detection system. Such a mounting part can for example be a glass slide and preferably the first part is optically bonded to the mount part using a suitable adhesive having a refractive index similar to that of the orifice carrying part of the plate. Preferably the surfaces and/or edges of the orifice carrying part and/or the mount part are treated so as to increase internal reflections, and optimise transfer of light to the detector or from the light source.
Another aspect of the invention provides a light waveguide or an optically transmissive plate for a particle detection system which plate comprises an orifice for allowing flow of particles through the plate and part of the extremities or surfaces of the plate are treated so as to increase internal optical reflections within the plate. The plate comprises an optically transparent region adjacent or surrounding the orifice thereby to allow input and output of light to and from the plate. Additionally, at least part of the extremities of the plate are also optically transparent to enable attachment of a light source or detector to said part.